1. Field of the Invention
The present invention relates to a pattern writing system, a pattern writing method, and an abnormality diagnosing method of the pattern writing system.
2. Background Art
Photomasks (also called reticles or masks, hereinafter referred to collectively as masks) for forming fine element circuit patterns of semiconductor integrated circuits (LSIs) or the like are manufactured by irradiating and exposing resists coated onto mask substrates with beams such as electron beams or laser beams, followed by development and etching. In addition, some semiconductor devices are manufactured by directly performing writing of circuit patterns onto semiconductor wafers with the beams.
In pattern writing systems using an energy beam, when abnormality of the writing position and an amount of irradiation caused by the pattern writing system or caused by an abnormality due to foreign substances on the substrate occurs, the abnormality is usually found in the inspection process of the written patterns. The pattern writing process may take 10 hours or more, during which time the writing is continued regardless of the occurrence of an abnormality. In addition, the inspection process is performed after the pattern forming process, including, not only the writing process, but also the developing process thereafter. Therefore, discovery of an abnormality or plurality of abnormalities after such process leads to significant waste of time and cost. In other words, if the same kind of abnormality occurs on all the substrates and the products written between the occurrence and discovery of the abnormality do not satisfy the shipping specifications, the writing time has been wasted. In addition, the continuation of the writing means delay in start of diagnosing of the abnormality, fixing and the recovery of the writing system. Further, when the product is used in the next process without detecting the abnormality in the inspection process, secondary damage in the wafer process, for example, may occur. For these reasons, abnormality is desired to be detected during the writing process.
For addressing this problem, a method for detecting abnormality of each shot during the writing process in a charged particle beam pattern writing system is disclosed. See for example, Japanese Patent Application Publication No. 3-24772 and Japanese Patent Application Laid-Open No. 5-74404).
Japanese Patent Application Publication No. 3-24772 discloses a charged particle beam exposure system in which an electron lens is arranged at a fixed angle from the main beam axis near an exposed material surface, reflected charged particles from the irradiated material surface are focused by the electron lens on a two-dimensional position detector. The output signal of the position detector and the pattern signal transmitted to a deflector are compared to detect abnormality of the exposing position.
In this publication, a method for detecting irradiation amount abnormality is also disclosed. The method includes detecting a total current of the position detector for a shot, calculating the shot area and the shot time from the electric signals to the shaping deflectors and the blanking deflectors to form the shot and comparing them.
In Japanese Patent Application Publication No. 3-24772, the signal from the position detector and the signals for irradiation amount are processed and compared shot by shot.
However, the detection of reflected electrons for every shot by each shot and processing corresponding electrical signals make the data amount enormous and the processing load is heavy. In particular, recently, while patterns for LSI have become more complicated increased in the pattern density, and the shot time per shot has been shortened. It is more difficult to realize the method of abnormality detection during writing for recent LSI patterns.
The present invention has been conceived in view of such problems. In other words, an object of the present invention is to provide a pattern writing system and a pattern writing method, which efficiently detects and treats an irradiation amount abnormality during pattern writing in real time. Further, an object of the present invention is to provide an abnormality diagnosing method including estimating the cause of the abnormality.
Other challenges and advantages of the present invention are apparent from the following description.